1. Field of the Invention
This invention relates to the identification of microorganisms, and more particularly relates to an enzyme substrate useful in identification of an organism by analysis of its enzyme content.
2. Background
Many disease states are the result of a bacterial invasion of a body tissue or fluid such as blood, urine, cerebrospinal fluid or synovial fluid. Successful treatment of such infections requires early diagnosis, and proper treatment cannot be initiated until accurate identification of the pathogen has been accomplished. This is made difficult in the early stages of the infection because the concentration of the pathogen is low.
Several procedures currently in use in hospital microbiology laboratories for bacterial identification are growth-based methods which generally require 18-24 hours or longer following isolation of an organism to achieve identification. In some situations, this length of time before identification can be life-threatening.
Identification of a pathogen by determination of which enzymes are present has been investigated. This method depends upon hydrolysis of fluorogenic or chromogenic substrates by enzymes expressed by the organism and is generally conducted by inoculating a panel of substrates and correlating the resulting fluorogenic or chromogenic profile with profiles developed with the same panel for known organisms. Representative of this method is the disclosure of Bascomb in U.S. Pat. No. 4,603,108.
Godsey et al., in Journal of Clinical Microbiology, 13, 483 (1981), discloses a method and apparatus for profiling enzymes expressed by strains of the family Enterobacteriaceae using fluorogenic substrates from .beta.-methylumbelliferone, .beta.-naphthylamine and 7-amino-4-methyl coumarin (AMC).
Tryptophanase is an enzyme, present in certain bacteria, that catalyzes the conversion of tryptophan to indole, pyruvic acid and ammonia. A substrate, S-(2-nitrophenyl) cysteine, which is cleaved by this enzyme to the chromophore 2-nitrothiophenol has been disclosed by Suelter et al., Methods in Enzymology 82, 561, (1979).
There is a need for a fluorogenic substrate for trypotophanase which could be included in enzyme profiling panels for bacterial identification. Such a substrate would greatly improve the accuracy of bacterial identification by this procedure, in particular for species of Enterobacteriaceae. It is toward fulfillment of this need that the present invention is directed.